Tamper resistant receptacles are known in the art. “Tamper Resistant” or “TR” receptacles are a class of electrical receptacle outlets configured to deny access to the device's electrical contacts unless force is applied simultaneously to both the hot and neutral plug openings of the device pursuant to NEC Code 406.11 et seq. The Code and related regulatory requirements provide that not only must the outlet openings remain blocked unless force is applied to both openings at the same time, but also that any foreign object 1/32 inch or larger, must be prevented from bypassing the blocking member of a plug opening.
As will be appreciated, these requirements were enacted in response to the phenomena of small children curiously inserting a small toy or metal object into the hot or neutral opening of a receptacle and suffering electrical shock, burns, or even death.
In meeting the standard and providing the level of protection sought from these devices, the art has gravitated towards a configuration of receptacles utilizing cooperating shutter members to block access beyond the faceplate openings of the outlet. Specifically, to ensure that force directed into only one of the two blade openings is prevented from reaching the electrical contact that lies beneath, a sliding shutter mechanism is spring-biased into a position blocking (or “shuttering”) the blade opening from underneath the faceplate. The shutter physically prevents an object entering the blade opening from reaching the electrical contact below that shutter. In order to allow the shutter of a respective blade opening to be uncovered, the spring-bias must be overcome by a camming action caused by the other plug blade during insertion in the other blade opening.
To this end, the most common prior art configuration of a TR receptacle includes a shutter assembly comprising a pair of cooperating shutters. Each of the shutters includes a blocking portion positioned below a respective one of the blade openings blocking access to the contacts. Each of the shutters also includes a cam portion that extends to the opposite blade opening that receives contact from a plug blade and translates the vertical force of a plug blade and camming action into a lateral sliding displacement of the blocking portion. Thus, force by vertical insertion of a plug-blade on the neutral blade opening will move the shutter from obstructing access to the electrical contact below the hot blade opening, and vice versa. Specifically, for example, during insertion of a plug, the neutral blade tine will cam against and past the shutter cam surface forcing the shutter cam arm to move laterally, thereby overcoming the spring bias of the shutter and causing the hot blade shutter blocking portion to slide into a position away from and revealing the electrical contact beneath the hot blade opening. Likewise, force on the hot blade opening will contact the cam surface and allow the blade to cam past and move the arm and compress the spring to move the shutter blocking portion that covers the neutral blade opening out of the way. As will be appreciated, with this configuration, when a child tries to insert a toy into either opening of the outlet, the blocking portion of the shutter remains immobile from the spring bias of the opposite shutter and prevents the child from reaching the electrical contact. However, when both blades of an electrical plug contact the shutters simultaneously, the simultaneous force and camming action allows both blades to continue their downward insertion by simultaneously sliding respective shutter blocking portions laterally out of the way of the electrical contacts of the opposite shutter until the blades cam past the shutters and are able to properly “plug in” to the outlet's internal face contacts.
Existing prior art TR receptacle designs and their operational details are available in U.S. Pat. No. 4,379,607 to Bowden, Jr.; U.S. Pat. No. 7,645,148 to Carbone et al.; and U.S. Publ. No. 2013/0295788 to Baldwin, et al. and the references cited therein, the entire contents of which are hereby incorporated by reference in their entirety.
The proliferation of these important safety devices has led to an appreciation of the issues affecting their effective life span. A presently appreciated issue recognized by the present inventors stems from the translation of the vertical force of the plug blade into lateral movement of the shutters. The issue here is two-fold. First, the shutter bodies have to slide over each other to move into the open position. A majority of the force required to effectuate such movement stems from the frictional forces at play of the various surfaces rubbing against one another as they attempt to move. Secondly, in most prior art shutter assemblies, there is no way to use the combined force of the insertion plug blades to overcome a spring bias. Rather, each plug blade opening and shutter operates against its own spring bias independently. Over time, the point of contact for the plug blades on each shutter may deform to the point that so much additional force is needed to slide the shutter open that the device is no longer deemed operable. Another presently appreciated issue recognized by the present inventors stems from the sharpness of plug blades being found on electrical products imported from overseas. As will be appreciated, during insertion of the plug blades into the outlet face openings, the vertical force of the incoming blades has the same point of contact on the cam surface. The cam surface of most prior art devices is an inclined “ramp” of about 45° that is of a length sufficient to cause lateral displacement during insertion of a distance that is equal to the entire distance necessary to un-shutter a blade opening (typically about 1.8 mm). Over time, these sharp blades having a single point of initial contact begin to deform and cut into the ramp surface which makes movement more difficult as the blades get stuck in divets or scratches at the point of contact. With each successive insertion, more and more force is needed to friction force the camming action and concomitant lateral sliding of the shutters. At some point, the deformity of the ramp surface may make insertion of a plug excessively difficult or even impossible. As this point, the device has reached the end of its useful life.
The foregoing underscores some of the problems associated with conventional TR receptacles. Furthermore, the foregoing highlights the long-felt, yet unresolved need in the art for a TR receptacle that may extend the useful life of the device. Moreover, the forgoing highlights the long-felt, yet unresolved need in the art for a TR receptacle that has an extended service life at a reasonable cost.